[drakaal]

Or you could just drop stop words and gerunds. This is another post from "TheTokenizer" that over simplifies a complex problem and creates devistatingly bad results.

The method described doesn't tell you what the sentence is about it tells you which things aren't verbs and articles and does a poor job of it.

Granted single sentence keyword extraction is not easy, but this is an awful approach. You'd be much better using Word Frequency analysis to determine the rarest words in the sentence.